Refractory Kawool

While getting ready to put Encore 0028 back together while looking at the manual I notice it wants Kawool in two 2 1/2" x5" gaps under the refractory, there wasn't any there when I took it apart. What does the Kawool do and is it necessary to put some there. Any idea where to get some.

Thanks

You can use regular gasket strips to put in its place, the later model encores don't have them. Nice to see some 0028's in existence. I found this bit about the Kawool in an old rebuild manual.